Vertical led with current-guiding structure

ABSTRACT

Techniques for controlling current flow in semiconductor devices, such as LEDs are provided. For some embodiments, a current-guiding structure may be provided including adjacent high and low contact areas. For some embodiments, a second current path (in addition to a current path between an n-contact pad and a substrate) may be provided. For some embodiments, both a current-guiding structure and second current path may be provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending U.S. patentapplication Ser. No. 13/161,254, filed Jun. 15, 2011, which is acontinuation of U.S. patent application Ser. No. 12/823,866 filed Jun.25, 2010, now issued as U.S. Pat. No. 8,003,994, which is a division ofU.S. patent application Ser. No. 12/136,547 filed Jun. 10, 2008, nowissued as U.S. Pat. No. 7,759,670, which claims the benefit of U.S.Provisional Patent Application Ser. No. 60/943,533, all of which areincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to semiconductorprocessing and, more particularly, to forming light-emitting diode (LED)structures.

2. Description of the Related Art

During the fabrication of light-emitting diodes (LEDs), an epitaxialstructure of an “LED stack” including layers of p-doped GaN and n-dopedGaN, for example, may be formed. FIG. 1 illustrates such an example of aconventional LED device 102, having an n-doped layer 106 and a p-dopedlayer 110 separated by a multi-quantum well (MQW) layer 108. The device102 is typically deposited on a carrier/growth-supporting substrate (notshown) of suitable material, such as c-plane silicon carbide (SiC) orc-plane sapphire, and bonded via a bonding layer 204 to a thermally andelectrically conductive substrate 101. A reflective layer 202 mayenhance brightness. Voltage may be applied between the n-doped layer 106and p-doped layer 110 via an n-electrode 117 and the conductivesubstrate 101, respectively.

In some cases, it may be desirable to control the amount of currentthrough the n-electrode 117 to the substrate 101, for example, to limitpower consumption and/or prevent damage to the device 102. Therefore, anelectrically insulative layer 206 may be formed below the p-doped layer110, in the reflective layer 202, to increase contact resistance belowthe n-electrode 117 and block current. The insulative layer 206 may besimilar to the current-blocking layer described in Photonics Spectra,December 1991, pp. 64-66 by H. Kaplan. In U.S. Pat. No. 5,376,580,entitled “Wafer Bonding of Light Emitting Diode Layers,” Kish et al.teach etching a patterned semiconductor wafer to form a depression andbonding the wafer to a separate LED structure such that the depressioncreates a cavity in the combined structure. When the combined structureis forward biased by applying voltage, current will flow in the LEDstructure, but no current will flow through the cavity or to the regiondirectly beneath the cavity since air is an electrical insulator. Thus,the air cavity acts as another type of current-blocking structure.

Unfortunately, these approaches to current guiding have a number ofdisadvantages. For example, the electrically insulative layer 206, theair cavity, and other conventional current-blocking structures may limitthermal conductivity, which may increase operating temperature andcompromise device reliability and/or lifetime.

Furthermore, a conventional LED device, such as the device 102 of FIG.1, may be susceptible to damage from electrostatic discharge (ESD) andother high voltage transients. ESD spikes may occur, for example, duringhandling of the device whether in fabrication of the LED device itself,in shipping, or in placement on a printed circuit board (PCB) or othersuitable mounting surface for electrical connection. Overvoltagetransients may occur during electrical operation of the LED device. Suchhigh voltage transients may damage the semiconductor layers of thedevice and may even lead to device failure, thereby decreasing thelifetime and the reliability of LED devices.

Accordingly, what is needed is an improved technique for guiding currentthrough an LED device.

SUMMARY OF THE INVENTION

Embodiments of the present invention generally provide techniques anddevices for guiding current in semiconductor devices, such aslight-emitting diodes (LEDs).

One embodiment of the present invention provides an LED. The LEDgenerally includes a substrate; an LED stack for emitting light disposedabove the substrate, wherein the LED stack comprises a p-typesemiconductor layer and an n-type semiconductor layer; an n-electrodedisposed above the n-type semiconductor layer; and an electricallyconductive material coupled between the substrate and the n-typesemiconductor layer and forming a non-ohmic contact with the n-typesemiconductor layer.

Another embodiment of the present invention provides an LED. The LEDgenerally includes a substrate; an LED stack for emitting light disposedabove the substrate, wherein the LED stack comprises a p-typesemiconductor layer and an n-type semiconductor layer; an n-electrodedisposed above the n-type semiconductor layer; a protective devicedisposed above the n-type semiconductor; and an electrically conductivematerial coupled between the substrate and the protective device.

Yet another embodiment of the present invention provides an LED. The LEDgenerally includes a substrate; a p-electrode disposed above thesubstrate and having first and second contacts, wherein the firstcontact has a higher electrical resistance than the second contact; anLED stack for emitting light disposed above the p-electrode, wherein theLED stack comprises a p-type semiconductor layer coupled to thep-electrode and an n-type semiconductor layer; and an n-electrodedisposed above the n-type semiconductor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 illustrates a prior art example light-emitting diode (LED) devicewith a current-guiding structure.

FIG. 2 illustrates an example LED device with a current-guidingstructure in accordance with embodiments of the present invention.

FIG. 3 illustrates an equivalent circuit to the LED device of FIG. 2.

FIG. 4 illustrates an example LED device with a second current path inaccordance with embodiments of the present invention.

FIG. 5 illustrates an equivalent circuit to the LED device of FIG. 4.

FIG. 6 illustrates an example LED device with a current-guidingstructure and a second current path in accordance with embodiments ofthe present invention.

FIG. 7 illustrates an equivalent circuit to the LED device of FIG. 6.

FIG. 8 illustrates an example LED device with a second current path witha protective device in accordance with embodiments of the presentinvention.

FIG. 9 illustrates an example LED device with a current-guidingstructure and a second current path with a protective device, inaccordance with embodiments of the present invention.

FIG. 10 illustrates an example LED device with a second current path, inchip form, in accordance with embodiments of the present invention.

FIG. 11 illustrates an example LED device with a second current path, inpackage form, in accordance with embodiments of the present invention.

FIG. 12 illustrates an example current vs. voltage (I-V) graph comparingLED devices with and without a second current path.

FIG. 13 illustrates an example graph of electrostatic discharge (ESD)level and corresponding survival rate of LED devices with and without asecond current path.

DETAILED DESCRIPTION

Embodiments of the present invention generally provide techniques forcontrolling current flow through a semiconductor device, such as alight-emitting diode (LED). The control may be via a current-guidingstructure, a second current path, or a combination thereof.

Hereinafter, relative terms such as “above,” “below,” “adjacent,”“underneath,” are for convenience of description and are typically notintended to require a particular orientation.

An Exemplary Current-Guiding Structure

FIG. 2 illustrates an example light-emitting diode (LED) device with acurrent-guiding structure in accordance with embodiments of the presentinvention. The device may include a device structure known as an LEDstack comprising any suitable semiconductor material for emitting light,such as AlInGaN. The LED stack may include a heterojunction composed ofa p-type semiconductor layer 110, an active layer 108 for emittinglight, and an n-type semiconductor layer 106. The LED stack may have atop surface 119, which may be roughened as shown in FIG. 2. The LEDdevice may comprise an n-electrode 117 formed on the top surface 119,the n-electrode 117 being electrically coupled to the n-typesemiconductor layer 106, and a p-electrode (a reflective layer 202 and abarrier metal layer 208 may function as the p-electrode) on the p-typesemiconductor layer 110.

Disposed adjacent to the p-type layer 110 may be a reflective layer 202interjected by a barrier metal layer 208 forming low contact resistanceareas 213 and a high contact resistance area 211, respectively. For someembodiments, the volume of the low contact resistance area 213 is largerthan the high contact resistance area 211. Electrically conductive, buthaving a higher electrical resistance than the low contact resistancearea 213, the high resistance contact area 211 may be formed utilizing ametallic material, as described below. The use and careful manipulationof areas with different levels of contact resistance may serve to directthe current to emit light from the active layer in desired areas, suchas light emission mainly from the active layer in areas that are notdisposed underneath the n-electrode 117 for enhanced light emission.

In this manner, the LED device of FIG. 2 with the fully electricallyconductive current-guiding structure may have greater thermalconductivity when compared to traditional LED devices with conventionalcurrent-blocking or other current-guiding structures, such as the LEDdevice of FIG. 1 with an electrically insulative layer 206. Therefore,the LED device of FIG. 2 and other embodiments of the present disclosurewith an electrically conductive current-guiding structure may enjoydecreased operating temperature and increased device reliability and/orlifetime when compared to such traditional LED devices.

FIG. 3 illustrates an equivalent circuit 300 for the LED device of FIG.2. As illustrated, the equivalent circuit 300 includes resistors R_(L)302 and R_(H) 304 in parallel that model the equivalent resistances ofthe high and low resistance contact areas 211, 213 of FIG. 2. Althoughonly one resistor is shown for the low contact resistance area 213, thisresistor R_(L) 302 may represent the lumped equivalent of one or moreparallel low contact resistance areas, such as the two areas 213 shownin FIG. 2. In a similar manner, the resistor R_(H) 304 may represent thelumped equivalent of one or more parallel high contact resistance areas211. For some embodiments, the equivalent high contact resistance may beat least two times the equivalent low contact resistance. Asillustrated, the parallel resistors, R_(L) 302 and R_(H) 304, are inseries with a diode 306 representing an ideal LED with no seriesresistance.

One or more layers of a substrate 201 may be disposed adjacent to thep-electrode (composed of the reflective layer 202 and the barrier metallayer 208 in FIG. 2). The substrate 201 may be electrically conductiveor semi-conductive. For some embodiments, the substrate 201 may bethermally conductive. A conductive substrate may be a single layer ormultiple layers and may comprise, for example, metal or metal alloys,such as Cu, Ni, Ag, Au, Al, Cu—Co, Ni—Co, Cu—W, Cu—Mo, Ge, Ni/Cu, orNi/Cu—Mo. Such a substrate may be deposited using any suitable thin filmdeposition technique, such as electrochemical deposition (ECD),electroless chemical deposition (Eless CD), chemical vapor deposition(CVD), metal organic CVD (MOCVD), and physical vapor deposition (PVD).For some embodiments, a seed metal layer may be deposited usingelectroless chemical deposition, and then one or more additional metallayers of the substrate 201 may be deposited above the seed metal layerusing electroplating. A semi-conductive substrate may comprise a singlelayer or multiple layers and may be composed of silicon (Si) or siliconcarbide (SiC), for example. The thickness of the substrate 201 may rangefrom about 10 to 400 μm.

The reflective layer 202 may comprise a single layer or multiple layerscomprising any suitable material for reflecting light and having arelatively low electrical resistance compared to materials used tocreate the high contact resistance area(s) 211. For example, thereflective layer 202 may comprise material such as silver (Ag), gold(Au), aluminum (Al), Ag—Al, silver (Ag), gold (Au), aluminum (Al),Ag—Al, Mg/Ag, Mg/Ag/Ni/, Mg/Ag/Ni/Au, AgNi, Ni/Ag/Ni/Au, Ag/Ni/Au,Ag/Ti/Ni/Au, Ti/Al, Ni/Al, AuBe, AuGe, AuPd, AuPt, AuZn, or using analloy containing Ag, Au, Al, nickel (Ni), chromium (Cr), magnesium (Mg),platinum (Pt), palladium (Pd), rhodium (Rh), or copper (Cu).

For some embodiments, the low contact resistance area(s) 213 maycomprise an omni-directional reflective (ODR) system. An ODR maycomprise a conductive transparent layer, composed of such materials asindium tin oxide (ITO) or indium zinc oxide (IZO), and a reflectivelayer. The ODR may be interjected by a current blocking structure orother suitable structure in an effort to direct the current. Anexemplary ODR system is disclosed in commonly-owned U.S. patentapplication Ser. No. 11/682,780, entitled “Vertical Light-Emitting DiodeStructure with Omni-Directional Reflector” and filed on Mar. 6, 2007,herein incorporated by reference in its entirety.

The n-electrode 117 (also known as a contact pad or n-pad) may be asingle metal layer or multiple metal layers composed of any suitablematerial for electrical conductivity, such as Cr/Au, Cr/Al, Cr/Al,Cr/Pt/Au, Cr/Ni/Au, Cr/Al/Pt/Au, Cr/Al/Ni/Au, Ti/Al, Ti/Au, Ti/Al/Pt/Au,Ti/Al/Ni/Au, Al, Al/Pt/Au, Al/Pt/Al, Al/Ni/Au, Al/Ni/Al, Al/W/Al,Al/W/Au, Al/TaN/Al, Al/TaN/Au, Al/Mo/Au. The thickness of then-electrode 117 may be about 0.1˜50 μm. The n-electrode 117 may beformed by deposition, sputtering, evaporation, electroplating,electroless plating, coating, and/or printing on the top surface 119 ofthe LED stack.

The barrier metal layer 208 may be a single layer or multiple layerscomprising any suitable material for forming the high contact resistancearea(s) 211. For example, the barrier metal layer 208 may comprisematerials such as Ag, Au, Al, molybdenum (Mo), titanium (Ti), hafnium(Hf), germanium (Ge), Mg, zinc (Zn), Ni, Pt, tantalum (Ta), tungsten(W), W—Si, W/Au, Ni/Cu, Ta/Au, Ni/Au, Pt/Au, Ti/Au, Cr/Au, Ti/Al, Ni/Al,Cr/Al, AuGe, AuZn, Ti/Ni/Au, W—Si/Au, Cr/W/Au, Cr/Ni/Au, Cr/W—Si/Au,Cr/Pt/Au, Ti/Pt/Au, Ta/Pt/Au, indium tin oxide (ITO), and indium zincoxide (IZO).

As illustrated in FIG. 2, protective layers 220 may be formed adjacentto the lateral surfaces of the LED device. These protective layers 220may serve as passivation layers in an effort to protect the LED device,and especially the heterojunction, from electrical and chemicalconditions in the environment.

The high and low contact resistance areas may be formed, for example, bydepositing one or more layers serving as the reflective layer 202 by anysuitable process, such as electrochemical deposition or electrolesschemical deposition. Areas designated for high contact resistance areas211 may be removed in the reflective layer 202 by any suitable process,such as wet etching or dry etching. Following removal of the designatedareas, a barrier metal layer 208 may be formed in the voided spaceswithin the reflective layer 202. For some embodiments as illustrated inFIG. 2, the barrier metal layer 208 composing the high contactresistance area(s) 211 may fill in the voided spaces within thereflective layer 202 and cover the reflective layer.

For some embodiments, the LED stack top surface 119 may be patterned orroughened to increase light extraction when compared to LED stacks witha smooth top surface. The top surface 119 may be patterned or roughenedusing any suitable technique (e.g., wet or dry etching).

For some embodiments, the current-guiding structure described herein maybe combined with a second current path as illustrated in FIGS. 6 and 9.This second current path is described in greater detail below, withreference to FIG. 4.

An Exemplary Second Current Path

FIG. 4 illustrates an example light-emitting diode (LED) device 400 witha second current path 402 in accordance with embodiments of the presentinvention. As illustrated, the LED device 400 may include a substrate201, a p-electrode 207 disposed above the substrate 201, an LED stack104 disposed above the p-electrode 207, and an n-electrode 117 disposedabove the LED stack 104. The substrate 201 may be thermally conductiveand electrically conductive or semi-conductive, as described above. TheLED stack 104 may include a heterojunction, which may comprise a p-typesemiconductor layer 110, an active layer 108 for emitting light, and ann-type semiconductor layer 106. A second electrically conductivematerial 411 may be coupled to the substrate 201 and to the n-typesemiconductor layer 106 to form a non-ohmic contact 412 with n-typesemiconductor layer 106 in an effort to provide a second current path402 between the substrate 201 and the n-semiconductor layer 106. Thesecond conductive material 411 may be formed via any suitable process,such as e-beam deposition, sputtering, and/or printing.

As illustrated, an electrically insulative layer 404 may separate thesecond conductive material 411 and at least a portion of the LED stack104. The insulative layer 404 may comprise any suitable electricallyinsulative material, such as SiO₂, Si₃N₄, TiO₂, Al₂O₃, HfO₂, Ta₂O₅,spin-on glass (SOG), MgO, polymer, polyimide, photoresistance, parylene,SU-8, and thermoplastic. For some embodiments, the protective layers 220may serve as the insulative layer 404.

As described above, the substrate 201 may be a single layer or multiplelayers comprising metal or metal alloys, such as Cu, Ni, Ag, Au, Al,Cu—Co, Ni—Co, Cu—W, Cu—Mo, Ge, Ni/Cu and Ni/Cu—Mo. The thickness of thesubstrate 201 may be about 10 to 400 μm.

FIG. 5 illustrates an equivalent circuit 500 for the LED device of FIG.4. As illustrated, the equivalent circuit 500 includes two parallelcurrent paths. The first current path includes an equivalent resistorR_(L) 502 in series with an ideal LED 504 forming a forward current pathfrom the substrate 201 to the n-electrode 117. The second current path402 is represented by a bidirectional transient voltage suppression(TVS) diode 506. The TVS diode 506 may operate similar to two opposingzener diodes connected in series and may serve to protect the resistor502 and ideal LED 504 from high voltage transients. The TVS diode 506can respond to over-voltages faster than other common over-voltageprotection components (e.g., varistors or gas discharge tubes) makingthe TVS diode 506 useful for protection against very fast and oftendamaging voltage transients, such as electrostatic discharge (ESD). Thesecond conductive material 411 of FIG. 4 may form the TVS diode 506 ofFIG. 5. The second conductive material 411 may shunt excess current ineither direction when the induced voltage exceeds the zener breakdownpotential.

FIG. 6 illustrates another example LED device with a second current path402 in accordance with embodiments of the present invention. Asillustrated, an LED device with a second current path 402 may alsoinclude the current-guiding structure resulting from separate high andlow resistance contact areas 211, 213. For example, these differentcontact areas may be formed by the interjection of the reflective layer202 by the barrier metal layer 208, as described above with respect toFIG. 2.

FIG. 7 illustrates an equivalent circuit 700 to the LED device of FIG.6. As illustrated, the single equivalent resistance R_(L) 502 of FIG. 5is replaced by the parallel combination of R_(H) 304 and R_(L) 302 torepresent adjacent high and low contact resistance areas 211, 213 ofFIG. 6. The remainder of the circuit 700 is equivalent to the circuit500 of FIG. 5. In other words, the LED device of FIG. 6 may have theadvantages of current guiding and transient suppression.

FIG. 8 illustrates another example LED device with a second current path402 in accordance with embodiments of the present invention. In thisembodiment, a protective device 810 is formed in the second current path402. As illustrated, the protective device 810 may be formed on then-type semiconductor layer 106 and may serve to increase the level oftransient voltage protection or the current capability, therebyincreasing the reliability and/or lifetime of the LED device. Theprotective device 810 may comprise any suitable material, such as ZnO,ZnS, TiO₂, NiO, SrTiO₃, SiO₂, Cr₂O₃, and polymethyl-methylacrylate(PMMA). The thickness of the protective device 810 may range from about1 nm to 10 μm.

As illustrated in FIG. 9, an LED device with a second current path 402and a protective device 810, as shown in FIG. 8, may also include acurrent-guiding structure resulting from separate high and lowresistance contact areas 211, 213. For example, these different contactareas may be formed by the interjection of the reflective layer 202 bythe barrier metal layer 208, as described above with respect to FIG. 2.

FIG. 10 illustrates an example LED device with a second current path, inchip form, in accordance with embodiments of the present invention. Asillustrated, a bonding metal layer 1002 may be deposited for electricalconnection above the protective device 810 in the second current path.The bonding layer 1002 may comprise any suitable material for electricalconnection, such as Al, Au, Ti/Au, Ti/Al, Ti/Pt/Au, Cr/Au, Cr/Al, Ni/Au,Ni/Al, or Cr/Ni/Au. The thickness of the bonding layer 1002 may rangefrom 0.5 to 10 μm. For some embodiments, the n-electrode 117 may beextended to allow bonding to a package, as described below with respectto FIG. 11.

FIG. 11 illustrates the LED device of FIG. 10 in package form, inaccordance with embodiments of the present invention. As illustrated,the substrate 201 may be bonded to a common package anode lead 1102. Thebonding layer 1002 may be coupled to the anode lead 1102 via a bondingwire 1104 attached to the bonding metal 1002, thereby forming the secondcurrent path. The n-electrode 117 may be coupled to a cathode packagelead 1106 via another bonding wire 1108.

FIG. 12 is a graph 1200 plotting example I-V curves 1204, 1202 of an LEDdevice with and without a second current path, respectively. Asillustrated by the I-V curve 1204, the second current path may allow anLED device to withstand higher voltage without an excessive amount ofcurrent, which may prevent damage and/or prolong device life.

FIG. 13 illustrates an example graph 1300 of ESD voltage andcorresponding survival rate of LED devices with and without a secondcurrent path. In the illustrated scenario, LED devices 1304, 1306, 1308,1310, 1312 without a second current path pass the test with varioussurvival rates at various ESD voltages. In contrast, LED devices 1302with the second current path pass at a rate at or near 100%, even athigher ESD voltage levels greater than 2000 V.

While the current-guiding structures described herein have advantagesthat apply to vertical light-emitting device (VLED) devices, thoseskilled in the art will recognize that such advantages generally applyto most semiconductor devices. Therefore, the structures describedherein may be used to advantage to form low resistance contacts and/ortransient suppressors for any type of semiconductor device having a p-njunction.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A light-emitting diode (LED), comprising: a substrate; an LED stackfor emitting light disposed above the substrate, wherein the LED stackcomprises: a p-type semiconductor layer; and an n-type semiconductorlayer disposed above the p-type semiconductor layer, wherein the LEDstack provides a first current path for the LED; and a second currentpath for the LED different from the first current path.
 2. The LED ofclaim 1, wherein the second current path is coupled between thesubstrate and the n-type semiconductor layer.
 3. The LED of claim 2,wherein the second current path forms a non-ohmic contact with then-type semiconductor layer.
 4. The LED of claim 2, wherein the secondcurrent path comprises an electrically conductive material.
 5. The LEDof claim 4, wherein the conductive material comprises multiple metallayers.
 6. The LED of claim 4, wherein the conductive material comprisesat least one of Ni, Ag, Au, Al, Mo, Pt, W, W—Si, Ta, Ti, Hf, Ge, Mg, Zn,W/Au, Ta/Au, Pt/Au, Ti/Au, Ti/Al, Ti/Pt/Au, Ti/Ni/Au, Ta/Pt/Au, W—Si/Au,Cr/Au, Cr/Al, Ni/Au, Ni/Al, Ni/Cu, Cr/Ni/Au, Cr/W/Au, Cr/W—Si/Au,Cr/Pt/Au, AuGe, AuZn, indium tin oxide (ITO), or indium zinc oxide(IZO).
 7. The LED of claim 2, further comprising an electricallyinsulative material between the second current path and the LED stack.8. The LED of clam 7, wherein the electrically insulative materialcomprises a passivation layer adjacent lateral surfaces of the LEDstack.
 9. The LED of claim 7, wherein the insulative material comprisesat least one of SiO₂, Si₃N₄, TiO₂, Al₂O₃, HfO₂, Ta₂O₅, spin-on glass(SOG), MgO, a polymer, polyimide, photoresist, parylene, SU-8, orthermoplastic.
 10. The LED of claim 1, wherein the second current pathis configured to protect the LED stack from a high-voltage transient.11. The LED of claim 10, wherein the high-voltage transient comprises anelectrostatic discharge (ESD).
 12. The LED of claim 2, wherein thesecond current path comprises a protective device disposed adjacent then-type semiconductor layer.
 13. The LED of claim 12, wherein theprotective device comprises at least one of ZnO, ZnS, TiO₂, NiO, SrTiO₃,SiO₂, Cr₂O₃, or polymethyl-methylacrylate (PMMA).
 14. The LED of claim12, wherein the thickness of the protective device is in a range from 1nm to 10 μm.
 15. The LED of claim 12, wherein the second current pathcomprises a bonding layer disposed adjacent the protective device. 16.The LED of claim 15, wherein the second current path comprises a wirecoupled between the substrate and the bonding layer.
 17. The LED ofclaim 15, wherein the bonding layer comprises multiple metal layers. 18.The LED of claim 15, wherein the bonding layer comprises at least one ofTi/Au, Ti/Al, Ti/Pt/Au, Cr/Au, Cr/Al, Al, Au, Ni/Au, Ni/Al, or Cr/Ni/Au.19. The LED of claim 15, wherein the thickness of the bonding layer isin a range from 0.5 to 10 μm.
 20. The LED of claim 1, further comprisinga p-electrode interposed between the substrate and the LED stack,wherein the p-electrode comprises an electrically conductive structurefor guiding current through the LED stack such that the light emitteddirectly underneath the n-electrode is less than the light emitted fromother areas of the LED stack.
 21. The LED of claim 20, wherein thecurrent-guiding structure comprises first and second contacts, the firstcontact having a higher electrical resistance than the second contact.22. A light-emitting diode (LED), comprising: an n-electrode; an LEDstack for emitting light disposed below the n-electrode, wherein the LEDstack comprises an n-type semiconductor layer coupled to the n-electrodeand a p-type semiconductor layer disposed below the n-type semiconductorlayer; and a p-electrode disposed below the p-type semiconductor layer,wherein the p-electrode comprises an electrically conductive structurefor guiding current through the LED stack such that the light emitteddirectly underneath the n-electrode is less than the light emitted fromother areas of the LED stack.
 23. The LED of claim 22, wherein thecurrent-guiding structure comprises first and second contacts, the firstcontact having a higher electrical resistance than the second contact.24. The LED of claim 23, wherein the first contact comprises a barriermetal layer.
 25. The LED of claim 23, wherein the first contactcomprises multiple metal layers.
 26. The LED of claim 23, wherein thefirst contact comprises at least one of Pt, tantalum (Ta), tungsten (W),W—Si, Ni, Cr/Ni/Au, W/Au, Ta/Au, Ni/Au, Ti/Ni/Au, W—Si/Au, Cr/W/Au,Cr/W—Si/Au, Pt/Au, Cr/Pt/Au, or Ta/Pt/Au.
 27. The LED of claim 23,wherein the second contact comprises a reflective layer.
 28. The LED ofclaim 23, wherein the second contact comprises at least one of silver(Ag), gold (Au), aluminum (Al), Ag—Al, Mg/Ag, Mg/Ag/Ni/, Mg/Ag/Ni/Au,AgNi, Ni/Ag/Ni/Au, Ag/Ni/Au, Ag/Ti/Ni/Au, Ti/Al, Ni/Al, AuBe, AuGe,AuPd, AuPt, AuZn, indium tin oxide (ITO), indium zinc oxide (IZO), or analloy containing at least one of Ag, Au, Al, nickel (Ni), magnesium(Mg), chromium (Cr), platinum (Pt), palladium (Pd), rhodium (Rh), orcopper (Cu).
 29. The LED of claim 23, wherein the second contactcomprises an omni-directional reflective (ODR) system.
 30. The LED ofclaim 23, wherein an area of the second contact is larger than an areaof the first contact.
 31. The LED of claim 23, wherein the first contactis disposed in a voided space of the second contact.
 32. The LED ofclaim 23, wherein the resistance of the first contact is at least doublethe resistance of the second contact.
 33. The LED of claim 22, furthercomprising a substrate disposed under and coupled to the p-electrode.34. The LED of claim 22, wherein the LED is a vertical light-emittingdiode (VLED).
 35. A light-emitting diode (LED), comprising: a substrate;a p-electrode disposed above the substrate; an LED stack for emittinglight disposed above the p-electrode, wherein the LED stack comprises: ap-type semiconductor layer coupled to the p-electrode; and an n-typesemiconductor layer disposed above the p-type semiconductor layer,wherein the LED stack provides a first current path for the LED; ann-electrode disposed above the n-type semiconductor layer, wherein thep-electrode comprises an electrically conductive structure for guidingcurrent through the LED stack such that the light emitted directlyunderneath the n-electrode is less than the light emitted from otherareas of the LED stack; and a second current path for the LED differentfrom the first current path, wherein the second current path is coupledbetween the substrate and the n-type semiconductor layer and wherein thesecond current path comprises a protective device disposed adjacent then-type semiconductor layer.
 36. The LED of claim 35, wherein thecurrent-guiding structure comprises first and second contacts, the firstcontact having a higher electrical resistance than the second contact.37. The LED of claim 35, wherein the protective device comprises atleast one of ZnO, ZnS, TiO₂, NiO, SrTiO₃, SiO₂, Cr₂O₃, orpolymethyl-methylacrylate (PMMA).